2.C.1 Feedback Mechanisms Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes.

Negative feedback mechanisms maintain dynamic homeostasis for a particular condition by returning the changing condition back to its target set point.

Negative feedback maintains stability around a target set point.

Example: Thermoregulation in animals

Example: Plant responses to water limitations Water loss, plant wilts ABA causes stomata to close Transpiration rate decreases Stomata Open Transpiration rate increases Example: Plant responses to water limitations

Positive feedback mechanisms amplify responses and processes in biological organisms. Global Warming Positive Feedback Loop

Example: Lactation in mammals

Example: Onset of labor in childbirth

Example: Ripening of fruit

Ethylene released by fruit Ethylene produced Fruit Ripens Ethylene released by fruit

Alteration in the mechanisms of feedback often results in dire consequences.

Example: Diabetes mellitus in response to decreased insulin.

Type 1 Diabetes: an autoimmune disease that results in the destruction of insulin-producing cells of the pancreas.

Type 2 Diabetes: diet-related insulin resistance brought on by too much sugar in the diet and lack of exercise.

Example: Graves’ disease (hyperthyroidism)

Learning Objectives: LO 2.15 The student can justify a claim made about the effect(s) on a biological system at the molecular, physiological or organismal level when given a scenario in which one or more components within a negative regulatory system is altered. [See SP 6.1] LO 2.16 The student is able to connect how organisms use negative feedback to maintain their internal environments. [See SP 7.2] LO 2.17 The student is able to evaluate data that show the effect(s) of changes in concentrations of key molecules on negative feedback mechanisms. [See SP 5.3] LO 2.18 The student can make predictions about how organisms use negative feedback mechanisms to maintain their internal environments. [See SP 6.4]

LO 2.19 The student is able to make predictions about how positive feedback mechanisms amplify activities and processes in organisms based on scientific theories and models. [See SP 6.4] LO 2.20 The student is able to justify that positive feedback mechanisms amplify responses in organisms. [See SP 6.1]